Method for making a semiconductor device having a high-k gate dielectric and a titanium carbide gate electrode

ABSTRACT

A method for making a titanium carbide layer is described. That method comprises alternately introducing a carbon containing precursor and a titanium containing precursor into a chemical vapor deposition reactor, while a substrate is maintained at a selected temperature. The reactor is operated for a sufficient time, and pulse times are selected for the carbon containing precursor and the titanium containing precursor, to form a titanium carbide layer of a desired thickness and workfunction on the substrate.

FIELD OF THE INVENTION

The present invention relates to methods for making semiconductordevices, in particular, those with titanium carbide containing gateelectrodes or barrier layers.

BACKGROUND OF THE INVENTION

An MOS field-effect transistor may include a high-k gate dielectric anda metal gate electrode. The metal gate electrode may comprise a titaniumcarbide layer, which may be formed on the high-k gate dielectric usingan atomic layer chemical vapor deposition (“ALCVD”) process. Although anALCVD process may be used to deposit such a layer on such a dielectric,it may be difficult to generate a titanium carbide layer with thedesired thickness and workfunction using such a process.

Accordingly, there is a need for an improved process for making asemiconductor device that includes a titanium carbide containing gateelectrode or barrier layer. There is a need for an ALCVD process thatmay be tailored to produce a titanium carbide layer with the desiredthickness and workfunction. The method of the present invention providessuch a process.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1 a–1 b represent cross-sections of structures that may be formedwhen carrying out an embodiment of the method of the present invention.

FIGS. 2 a–2 i represent cross-sections of structures that may be formedwhen carrying out an embodiment of the method of the present inventionto make a semiconductor device using a replacement metal gate process.

Features shown in these figures are not intended to be drawn to scale.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

A method for making a titanium carbide layer is described. That methodcomprises alternately introducing a carbon containing precursor and atitanium containing precursor at selected pulse times into a chemicalvapor deposition reactor, while maintaining a substrate at a selectedtemperature. The reactor is operated for a sufficient time, and pulsetimes are selected for the carbon containing precursor and the titaniumcontaining precursor, to form a titanium carbide layer of a desiredthickness and workfunction on the substrate.

In the following description, a number of details are set forth toprovide a thorough understanding of the present invention. It will beapparent to those skilled in the art, however, that the invention may bepracticed in many ways other than those expressly described here. Theinvention is thus not limited by the specific details disclosed below.

FIGS. 1 a–1 b represent cross-sections of structures that may be formedwhen carrying out an embodiment of the method of the present invention.FIG. 1 a represents substrate 100 upon which is formed high-k gatedielectric layer 101 and titanium carbide layer 102. Substrate 100 maycomprise any material that may serve as a foundation upon which asemiconductor device may be built. Substrate 100 may, for example,comprise silicon and/or germanium.

High-k gate dielectric layer 101 may comprise, for example, hafniumoxide, hafnium silicon oxide, lanthanum oxide, lanthanum aluminum oxide,zirconium oxide, zirconium silicon oxide, titanium oxide, tantalumoxide, barium strontium titanium oxide, barium titanium oxide, strontiumtitanium oxide, yttrium oxide, aluminum oxide, lead scandium tantalumoxide, and lead zinc niobate. Particularly preferred are hafnium oxide,lanthanum oxide, zirconium oxide, and aluminum oxide. Although a fewexamples of materials that may be used to form high-k gate dielectriclayer 101 are described here, that layer may be made from othermaterials that serve to reduce gate leakage.

High-k gate dielectric layer 101 may be formed on substrate 100 using aconventional ALCVD process. In such a process, a metal oxide precursor(e.g., a metal chloride) and steam may be alternately fed at selectedflow rates into a CVD reactor, which is operated at a selected pressurewhile substrate 100 is maintained at a selected temperature. The CVDreactor should be operated long enough to form a layer with the desiredthickness. In most applications, dielectric layer 101 should be lessthan about 40 angstroms thick, and more preferably between about 5angstroms and about 20 angstroms thick.

In the method of the present invention, titanium carbide layer 102 isformed on high-k gate dielectric layer 101 by alternately introducing acarbon containing precursor and a titanium containing precursor into aCVD reactor, while substrate 100 is maintained at a selectedtemperature. Pulse times should be selected for the carbon containingprecursor and the titanium containing precursor, and the reactor shouldbe operated for a sufficient time, to generate a titanium carbide layerof a desired thickness and workfunction.

The carbon containing precursor may comprise a metal alkyl or metalloidalkyl complex, such as trimethylaluminum (“TMA”) or triethylboron. Thetitanium containing precursor may comprise a titanium halide, such astitanium tetrachloride (“TiCl₄”). The pulse time for the carboncontaining precursor for a given growth cycle, when introduced into theCVD reactor, may be less than about 1 second, on the order of 10 to 20seconds, or somewhere in between—depending upon whether the desiredtitanium carbide layer will be a p-type, n-type, or mid-gap film.

The pulse time for the titanium containing precursor should besufficient to provide enough titanium to generate the desired titaniumcarbide layer. In many applications, a pulse time between about 2 and 3seconds should be adequate. The substrate temperature preferably shouldbe maintained at between about 100° C. and about 700° C. The optimumsubstrate temperature, like the optimum pulse time for the carboncontaining precursor, may depend upon whether the desired titaniumcarbide layer will be a p-type, n-type, or mid-gap film.

The method of the present invention may be tailored to produce titaniumcarbide layers with different thicknesses and workfunctions. Forexample, to form a p-type titanium carbide layer, the temperature ofsubstrate 100 preferably should be maintained between about 100° C. andabout 250° C. To form a p-type titanium carbide layer using a TMAprecursor, that precursor preferably should be introduced into thereactor for a relatively short pulse time, e.g., a pulse time that isbetween about 0.5 seconds and about 1 second. As mentioned above, thetitanium containing precursor (e.g., titanium tetrachloride) may have apulse time that is between about 2 and 3 seconds.

When titanium carbide layer 102 will set the workfunction for a PMOSgate electrode, titanium carbide layer 102 must be sufficiently thick toset the workfunction for the gate electrode. To form a sufficientlythick titanium carbide layer, a minimum number of growth cycles (eachgrowth cycle comprising a TMA pulse followed by a purging gas pulse, anda TiCl₄ pulse followed by a purging gas pulse) must be performed. Aftercompleting between about 20 and about 40 growth cycles using theoperating conditions described above, a p-type titanium carbide layerthat is between about 10 angstroms and about 20 angstroms thick, andthat sets a workfunction that is between about 4.9 eV and about 5.2 eV,may result.

If, alternatively, titanium carbide layer 102 should be an n-type layer,the temperature of substrate 100 preferably should be maintained aboveabout 400° C. (e.g., between about 400° C. and about 700° C.) whenforming that layer. To form an n-type titanium carbide layer using a TMAprecursor, that precursor preferably should be introduced into thereactor for a relatively long pulse time, e.g., a pulse time that isbetween about 10 seconds and about 20 seconds. In some embodiments, asingle pulse of TMA per growth cycle may be preferred; whereas, in otherembodiments, multiple pulses of TMA per growth cycle (e.g., fourseparate 5 second pulses per growth cycle instead of a single 20 secondpulse per growth cycle) may be preferred.

When forming an n-type titanium carbide layer using the method of thepresent invention, as when forming a p-type titanium carbide layer, thetitanium containing precursor (e.g., titanium tetrachloride) may have apulse time that is between about 2 and 3 seconds. One may form an n-typetitanium carbide layer that is between about 50 angstroms and about 250angstroms thick by completing between about 70 and about 250 growthcycles using these operating conditions. An n-type titanium carbidelayer with that thickness may set a workfunction for an NMOS gateelectrode that is between about 3.9 eV and about 4.3 eV.

When forming a titanium carbide layer with a mid-gap workfunction usingthe method of the present invention, the temperature of substrate 100preferably should be maintained between about 250° C. and about 400° C.To make such a mid-gap titanium carbide layer, the pulse time for thecarbon containing precursor preferably lies between the pulse times thatmay be applied when making p-type or n-type titanium carbide layers.Similarly, the number of growth cycles that may be required to form amid-gap titanium carbide layer of the desired thickness may lie betweenthe number of growth cycles required to make p-type or n-type titaniumcarbide layers.

FIG. 1 b represents a semiconductor device that includes NMOS gateelectrode 115 and PMOS gate electrode 120. NMOS gate electrode 115comprises n-type titanium carbide layer 105. PMOS gate electrode 120comprises p-type titanium carbide layer 110. N-type titanium carbidelayer 105 and p-type titanium carbide layer 110 are each formed onhigh-k gate dielectric layer 101. Metal layer 121 is formed on n-typetitanium carbide layer 105 and metal layer 118 is formed on p-typetitanium carbide layer 110. Metal layers 121 and 118 may comprise, forexample, titanium nitride. A replacement metal gate process, which maybe used to form a structure like the one that FIG. 1 b illustrates, isdescribed in detail below.

Although the method of the present invention may be used to form a metalgate electrode that includes a titanium carbide layer, the method mayalternatively be used to form titanium carbide containing barrier layersor liners. Such barrier layers or liners may serve to insulate one filmfrom another to prevent them from reacting. When forming a titaniumcarbide barrier layer using the method of the present invention, it maybe desirable to use triethylboron instead of TMA to generate a titaniumcarbide film with less impurity. Such a titanium carbide barrier layermay be relatively thin, e.g., between about 10 angstroms and about 40angstroms thick.

FIGS. 2 a–2 i illustrate how the method of the present invention may beapplied to make a semiconductor device using a replacement metal gateprocess. FIG. 2 a represents an intermediate structure that may beformed when making a CMOS device. That structure includes first part 201and second part 202 of substrate 200. Isolation region 203 separatesfirst part 201 from second part 202. Polysilicon layers 204 and 206 areformed on dielectric layers 205 and 207, respectively. Polysilicon layer204 is bracketed by sidewall spacers 208 and 209, and polysilicon layer206 is bracketed by sidewall spacers 210 and 211. Dielectric 212separates layers 204 and 206.

Substrate 200 may comprise any material that may serve as a foundationupon which a semiconductor device may be built. Isolation region 203 maycomprise silicon dioxide, or other materials that may separate thetransistor's active regions. Dielectric layers 205 and 207 may eachcomprise silicon dioxide, or other materials that may insulate thesubstrate from other substances. Polysilicon layers 204 and 206preferably are each between about 100 and about 2,000 angstroms thick,and more preferably between about 500 and about 1,600 angstroms thick.In this embodiment, polysilicon layer 204 is doped n-type (e.g., witharsenic, phosphorus or another n-type material), while polysilicon layer206 is doped p-type (e.g., with boron or another p-type material).Spacers 208, 209, 210, and 211 preferably comprise silicon nitride,while dielectric 212 may comprise silicon dioxide or a low-k material.

Conventional process steps, materials, and equipment may be used togenerate the FIG. 2 a structure, as will be apparent to those skilled inthe art. As shown, dielectric 212 may be polished back, e.g., via aconventional CMP step, to expose polysilicon layers 204 and 206.Although not shown, the FIG. 2 a structure may include many otherfeatures (e.g., a silicon nitride etch stop layer, source and drainregions, and one or more buffer layers) that may be formed usingconventional processes.

After forming the FIG. 2 a structure, n-type polysilicon layer 204 isremoved. In a preferred embodiment, that layer is removed by applying awet etch process. Such a wet etch process may comprise exposing layer204 to an aqueous solution that comprises a source of hydroxide for asufficient time at a sufficient temperature to remove substantially allof that layer without removing a significant amount of p-typepolysilicon layer 206. That source of hydroxide may comprise betweenabout 2 and about 30 percent ammonium hydroxide or a tetraalkyl ammoniumhydroxide, e.g., tetramethyl ammonium hydroxide (“TMAH”), by volume indeionized water.

N-type polysilicon layer 204 may be removed by exposing it to asolution, which is maintained at a temperature between about 15° C. andabout 90° C. (and preferably below about 40° C.), that comprises betweenabout 2 and about 30 percent ammonium hydroxide by volume in deionizedwater. During that exposure step, which preferably lasts at least oneminute, it may be desirable to apply sonic energy at a frequency ofbetween about 10 KHz and about 2,000 KHz, while dissipating at betweenabout 1 and about 10 watts/cm². For example, if n-type polysilicon layer204 is about 1,350 angstroms thick, it may be removed by exposing it atabout 25° C. for about 30 minutes to a solution that comprises about 15percent ammonium hydroxide by volume in deionized water, while applyingsonic energy at about 1,000 KHz—dissipating at about 5 watts/cm².

After removing n-type polysilicon layer 204, dielectric layer 205 isremoved. If dielectric layer 205 comprises silicon dioxide, it may beremoved using an etch process that is selective for silicon dioxide.Such an etch process may comprise exposing layer 205 to a solution thatincludes about 1 percent HF in deionized water. The time layer 205 isexposed should be limited, as the etch process for removing that layermay also remove part of dielectric layer 212. With that in mind, if a 1percent HF based solution is used to remove layer 205, the devicepreferably should be exposed to that solution for less than about 60seconds, and more preferably for about 30 seconds or less. As shown inFIG. 2 b, removal of dielectric layer 205 forms trench 213 withindielectric layer 212 positioned between sidewall spacers 208 and 209.

After removing dielectric layer 205, high-k gate dielectric layer 215 isformed within trench 213 and on substrate 200. Any of the materialsidentified above may be used to make high-k gate dielectric layer 215.High-k gate dielectric layer 215 may be formed using a conventionalALCVD process, as described above. High-k gate dielectric layer 215preferably should be less than about 40 angstroms thick, and morepreferably between about 5 angstroms and about 20 angstroms thick. Asshown in FIG. 2 c, when an ALCVD process is used to form high-k gatedielectric layer 215, that layer will form on the sides of trench 213 inaddition to forming on the bottom of that trench, and will form ondielectric layer 212.

In the illustrated embodiment, n-type titanium carbide layer 216 isformed directly on high-k gate dielectric layer 215 to generate the FIG.2 d structure. Like high-k gate dielectric layer 215, part of n-typetitanium carbide layer 216 lines trench 213 while part of that layerspills over onto dielectric layer 212. When forming n-type titaniumcarbide layer 216 on high-k gate dielectric layer 215 using an ALCVDprocess, the temperature of substrate 200 preferably is maintained aboveabout 400° C. While maintaining substrate 200 at the appropriatetemperature, TMA and TiCl₄ are alternately pulsed into the reactor. Thepulse time for TMA is preferably between about 10 seconds and about 20seconds. That pulse time may reflect a single pulse of TMA per growthcycle or, alternatively, multiple pulses of TMA per growth cycle.

When forming n-type titanium carbide layer 216, TiCl₄ may have a pulsetime that is between about 2 and 3 seconds. By continuing this processfor between about 70 and about 250 growth cycles, n-type titaniumcarbide layer 216 may reach a thickness that is between about 50angstroms and about 250 angstroms. The resulting n-type titanium carbidelayer may have a workfunction that is between about 3.9 eV and about 4.3eV.

In this embodiment, after forming n-type titanium carbide layer 216 onhigh-k gate dielectric layer 215, fill metal 221 is formed on n-typetitanium carbide layer 216. Fill metal 221 fills the remainder of trench213 and covers dielectric layer 212, as illustrated in FIG. 2 e. Fillmetal 221 preferably comprises a material that may be easily polished,and preferably is deposited over the entire device using a conventionalmetal deposition process. Such a fill metal may comprise, for example,titanium nitride, tungsten, titanium, aluminum, tantalum, tantalumnitride, cobalt, copper, or nickel.

In a particularly preferred embodiment, fill metal 221 comprisestitanium nitride. Titanium nitride may be deposited using an appropriateCVD or PVD process that does not significantly affect underlying n-typetitanium carbide layer 216 or high-k gate dielectric layer 215. Inaddition, when polysilicon layer 206 is subsequently removed (asdescribed below), titanium nitride may be more resistant than othermetals to the etch chemistry used to remove that layer.

After forming the FIG. 2 e structure, fill metal 221, n-type titaniumcarbide layer 216, and high-k gate dielectric layer 215 are removed fromabove dielectric layer 212 to generate the FIG. 2 f structure. Anappropriate CMP or etch process may be used to remove those layers fromdielectric layer 212. In a preferred embodiment, a combination of CMPand etch processes are used, e.g., a CMP step to remove fill metal 221followed by an etch step (or steps) to remove n-type titanium carbidelayer 216 and high-k gate dielectric layer 215.

After removing fill metal 221, n-type titanium carbide layer 216, andhigh-k gate dielectric layer 215 from above dielectric layer 212, p-typepolysilicon layer 206 is removed. P-type polysilicon layer 206 may beremoved selectively to fill metal 221 by exposing layer 206 to asolution that comprises between about 20 and about 30 percent TMAH byvolume in deionized water for a sufficient time at a sufficienttemperature (e.g., between about 60° C. and about 90° C.), whileapplying sonic energy.

After removing polysilicon layer 206, dielectric layer 207 is removed,e.g., by using the same process that was used to remove dielectric layer205. Removing dielectric layer 207 generates trench 214, as FIG. 2 gillustrates. Following the removal of that dielectric layer, high-k gatedielectric layer 217 is formed within trench 214 and onto dielectriclayer 212. The same process steps and materials used to form high-k gatedielectric layer 215 may be used to form high-k gate dielectric layer217.

In this embodiment, p-type titanium carbide layer 220 is then depositedon high-k gate dielectric layer 217. Like n-type titanium carbide layer216, p-type titanium carbide layer 220 may be formed using an ALCVDprocess. Unlike the process for forming n-type titanium carbide layer216, however, when forming p-type titanium carbide layer 220, substrate200 preferably should be maintained at a substantially lowertemperature, e.g., between about 100° C. and about 250° C.

In this embodiment, TMA and TiCl₄ are alternately pulsed into thereactor while maintaining substrate 200 at the appropriate temperature.The pulse time for TMA is preferably between about 0.5 seconds and about1 second and the pulse time for TiCl₄ may be between about 2 and 3seconds. By continuing this process for between about 20 and about 40growth cycles, p-type titanium carbide layer 220 may reach a thicknessthat is between about 10 angstroms and about 20 angstroms. The resultingp-type titanium carbide layer may have a workfunction that is betweenabout 4.9 eV and about 5.2 eV.

After forming p-type titanium carbide layer 220 on high-k gatedielectric layer 217, fill metal 218 may be formed on p-type titaniumcarbide layer 220 to generate the FIG. 2 h structure. The same processsteps and materials used to form fill metal 221 may be used to form fillmetal 218. In a preferred embodiment, fill metal 218 comprises titaniumnitride. Fill metal 218, p-type titanium carbide layer 220 and high-kgate dielectric layer 217 are then removed from dielectric layer 212 togenerate the FIG. 2 i structure. The same CMP and/or etch steps used toremove fill metal 221, n-type titanium carbide layer 216 and high-k gatedielectric layer 215 from above dielectric layer 212 may be used toremove fill metal 218, p-type titanium carbide layer 220 and high-k gatedielectric layer 217 from above dielectric layer 212.

After removing fill metal 218, p-type titanium carbide layer 220 andhigh-k gate dielectric layer 217 from above dielectric layer 212, acapping dielectric layer (not shown) may be deposited onto the resultingstructure using a conventional deposition process. Process steps forcompleting the device that follow the deposition of such a cappingdielectric layer, e.g., forming the device's contacts, metalinterconnect, and passivation layer, are well known to those skilled inthe art and will not be described here. Although a few examples ofprocess steps for forming the FIG. 2 i structure are presented here,many other process steps may be used to make that structure, as will beapparent to those skilled in the art.

The method of the present invention may enable one to make titaniumcarbide layers with different thicknesses and workfunctions, which maybe used in various applications. Although the foregoing description hasspecified certain steps and materials that may be used in the method ofthe present invention, those skilled in the art will appreciate thatmany modifications and substitutions may be made. Accordingly, all suchmodifications, substitutions and additions fall within the spirit andscope of the invention as defined by the appended claims.

1. A method for making a titanium carbide layer comprising: alternatelyintroducing a carbon containing precursor and a titanium containingprecursor at selected pulse times into a chemical vapor depositionreactor, while a substrate is maintained at a selected temperature;wherein the reactor is operated for a sufficient time, and pulse timesare selected for the carbon containing precursor and the titaniumcontaining precursor, to form a titanium carbide layer of a desiredthickness and workfunction on the substrate; wherein, the titaniumcarbide layer is between about 10 angstroms and about 20 angstromsthick, and is a p-type titanium carbide layer; the selected temperatureis between about 100° C. and about 250° C.; and the pulse time for thecarbon containing precursor is between about 0.5 seconds and about 1second.
 2. A method for making a semiconductor device comprising:forming a high-k gate dielectric layer on a substrate; and forming atitanium carbide containing gate electrode on the high-k gate dielectriclayer by: alternately introducing a carbon containing precursor and atitanium containing precursor at selected pulse times into a chemicalvapor deposition reactor, while the substrate is maintained at atemperature that is between about 100° C. and about 700° C.; wherein thepulse time for the carbon containing precursor is between about 0.5seconds and about 20 seconds; and wherein the reactor is operated for asufficient time to generate a titanium carbide layer that is betweenabout 10 angstroms and about 250 angstroms thick.
 3. The method of claim2 wherein the carbon containing precursor is selected from the groupconsisting of trimethylaluminum and triethylboron, and the titaniumcontaining precursor comprises titanium tetrachloride.
 4. The method ofclaim 2 wherein the high-k gate dielectric layer comprises a materialthat is selected from the group consisting of hafnium oxide, hafniumsilicon oxide, lanthanum oxide, lanthanum aluminum oxide, zirconiumoxide, zirconium silicon oxide, titanium oxide, tantalum oxide, bariumstrontium titanium oxide, barium titanium oxide, strontium titaniumoxide, yttrium oxide, aluminum oxide, lead scandium tantalum oxide, andlead zinc niobate.
 5. The method of claim 2 wherein: the titaniumcarbide layer is between about 10 angstroms and about 20 angstromsthick, and is a p-type titanium carbide layer; the selected temperatureis between about 100° C. and about 250° C.; and the pulse time for thecarbon containing precursor is between about 0.5 seconds and about 1second.
 6. The method of claim 2 wherein: the titanium carbide layer isbetween about 50 angstroms and about 250 angstroms thick, and is ann-type titanium carbide layer; the selected temperature is greater thanabout 400° C.; and the pulse time for the carbon containing precursor isbetween about 10 seconds and about 20 seconds.
 7. A method for making asemiconductor device comprising: forming a dielectric layer on asubstrate; forming a first trench and a second trench within thedielectric layer; forming a high-k gate dielectric layer within thefirst trench and within the second trench; forming an n-type titaniumcarbide layer on the high-k gate dielectric layer and within the firsttrench; and forming a p-type titanium carbide layer on the high-k gatedielectric layer and within the second trench.
 8. The method of claim 7wherein the high-k gate dielectric layer comprises a material that isselected from the group consisting of hafnium oxide, hafnium siliconoxide, lanthanum oxide, lanthanum aluminum oxide, zirconium oxide,zirconium silicon oxide, tantalum oxide, titanium oxide, bariumstrontium titanium oxide, barium titanium oxide, strontium titaniumoxide, yttrium oxide, aluminum oxide, lead scandium tantalum oxide, andlead zinc niobate.
 9. The method of claim 7 wherein the high-k gatedielectric layer comprises a material that is selected from the groupconsisting of hafnium oxide, lanthanum oxide, zirconium oxide, andaluminum oxide.
 10. The method of claim 7 wherein the n-type titaniumcarbide layer is formed on the high-k gate dielectric layer within thefirst trench before the p-type titanium carbide layer is formed on thehigh-k gate dielectric layer within the second trench.
 11. The method ofclaim 7 wherein the n-type titanium carbide layer is between about 50angstroms and about 250 angstroms thick, and has a workfunction that isbetween about 3.9 eV and about 4.2 eV.
 12. The method of claim 7 whereinthe p-type titanium carbide layer is between about 10 angstroms andabout 20 angstroms thick, and has a workfunction that is between about4.9 eV and about 5.2 eV.
 13. The method of claim 7 further comprisingforming a first fill metal on the n-type titanium carbide layer andforming a second fill metal on the p-type titanium carbide layer. 14.The method of claim 13 wherein the first fill metal is selected from thegroup consisting of titanium nitride, tungsten, titanium, aluminum,tantalum, tantalum nitride, cobalt, copper, and nickel; and the secondfill metal comprises titanium nitride.
 15. The method of claim 7wherein: the n-type titanium carbide layer is formed by alternatelyintroducing a trimethylaluminum precursor at a first selected pulsetime, and a titanium tetrachloride precursor at a second selected pulsetime, into a chemical vapor deposition reactor, while the substrate ismaintained at a temperature that is greater than about 400° C.; and thep-type titanium carbide layer is formed by alternately introducing atrimethylaluminum precursor at a third selected pulse time that isshorter than the first selected pulse time, and a titanium tetrachlorideprecursor at a fourth selected pulse time, into a chemical vapordeposition reactor, while the substrate is maintained at a temperaturethat is between about 100° C. and about 250° C.
 16. The method of claim15 wherein: the first selected pulse time is between about 10 secondsand about 20 seconds; the third selected pulse time is between about 0.5seconds and about 1 second; between about 70 and about 250 growth cyclesare performed to form the n-type titanium carbide layer; and betweenabout 20 and about 40 growth cycles are performed to form the p-typetitanium carbide layer.
 17. A method for making a semiconductor devicecomprising: forming a gate dielectric layer on a semiconductorsubstrate; and forming a gate electrode on said gate dielectric layer,wherein said gate electrode is comprised of a titanium carbide layer,wherein said titanium carbide layer is formed by alternately introducinga carbon containing precursor and a titanium containing precursor atselected pulse times into a chemical vapor deposition reactor at aselected temperature, and wherein said carbon containing precursorcomprises a compound that is selected from the group consisting of ametal alkyl complex and a metalloid alkyl complex, and said titaniumcontaining precursor comprises a titanium halide.
 18. A method formaking a semiconductor device comprising: forming a gate dielectriclayer on a semiconductor substrate; and forming a gate electrode on saidgate dielectric layer, wherein said gate electrode is comprised of atitanium carbide layer, wherein said titanium carbide layer is formed byalternately introducing a carbon containing precursor and a titaniumcontaining precursor at selected pulse times into a chemical vapordeposition reactor at a selected temperature, and wherein said titaniumcarbide layer has a p-type workfunction.
 19. A method for making asemiconductor device comprising: forming a gate dielectric layer on asemiconductor substrate; and forming a gate electrode on said gatedielectric layer, wherein said gate electrode is comprised of a titaniumcarbide layer, wherein said titanium carbide layer is formed byalternately introducing a carbon containing precursor and a titaniumcontaining precursor at selected pulse times into a chemical vapordeposition reactor at a selected temperature, and wherein said titaniumcarbide layer has a workfunction between about 4.9 eV and about 5.2 eV.20. The method of claim 19 wherein: said titanium carbide layer isbetween about 10 angstroms and about 20 angstroms thick; the selectedpulse time for said carbon containing precursor is between about 0.5seconds and about 1 second; and said selected temperature is betweenabout 100° C. and about 250° C.
 21. The method of claim 20 wherein saidcarbon containing precursor comprises a compound that is selected fromthe group consisting of a metal alkyl complex and a metalloid alkylcomplex, and said titanium containing precursor comprises a titaniumhalide.
 22. A method for making a semiconductor device comprising:forming a gate dielectric layer on a semiconductor substrate; andforming a gate electrode on said gate dielectric layer, wherein saidgate electrode is comprised of a titanium carbide layer, wherein saidtitanium carbide layer is formed by alternately introducing a carboncontaining precursor and a titanium containing precursor at selectedpulse times into a chemical vapor deposition reactor at a selectedtemperature, and wherein said titanium carbide layer has an n-typeworkfunction.
 23. A method for making a semiconductor device comprising:forming a gate dielectric layer on a semiconductor substrate; andforming a gate electrode on said gate dielectric layer, wherein saidgate electrode is comprised of a titanium carbide layer, wherein saidtitanium carbide layer is formed by alternately introducing a carboncontaining precursor and a titanium containing precursor at selectedpulse times into a chemical vapor deposition reactor at a selectedtemperature, and wherein said titanium carbide layer has a workfunctionbetween about 3.9 eV and about 4.3 eV.
 24. The method of claim 23wherein: said titanium carbide layer is between about 50 angstroms andabout 250 angstroms thick; the selected pulse time for said carboncontaining precursor is between about 10 seconds and about 20 seconds;and said selected temperature is between about 400° C. and about 700° C.25. The method of claim 24 wherein said carbon containing precursorcomprises a compound that is selected from the group consisting of ametal alkyl complex and a metalloid alkyl complex, and said titaniumcontaining precursor comprises a titanium halide.
 26. A method formaking a semiconductor device comprising: forming a gate dielectriclayer on a semiconductor substrate; and forming a gate electrode on saidgate dielectric layer, wherein said gate electrode is comprised of atitanium carbide layer, wherein said titanium carbide layer is formed byalternately introducing a carbon containing precursor and a titaniumcontaining precursor at selected pulse times into a chemical vapordeposition reactor at a selected temperature, and wherein said titaniumcarbide layer has a mid-gap workfunction.
 27. The method of claim 26wherein: the selected pulse time for said carbon containing precursor isbetween about 1 second and about 10 seconds; and said selectedtemperature is between about 250° C. and about 400° C.
 28. The method ofclaim 27 wherein said carbon containing precursor comprises a compoundthat is selected from the group consisting of a metal alkyl complex anda metalloid alkyl complex, and said titanium containing precursorcomprises a titanium halide.
 29. A method for making a semiconductordevice comprising: forming a trench in a dielectric layer; and forming agate electrode on a gate dielectric layer in said trench, wherein saidgate electrode is comprised of a titanium carbide layer, and whereinsaid titanium carbide layer is formed by alternately introducing acarbon containing precursor and a titanium containing precursor atselected pulse times into a chemical vapor deposition reactor at aselected temperature.
 30. The method of claim 29 wherein said trench isformed by using a selective etch process to remove a polysilicon gateelectrode from said dielectric layer.
 31. The method of claim 30 whereinsaid gate dielectric layer is a high-k gate dielectric layer thatcomprises a material that is selected from the group consisting ofhafnium oxide, hafnium silicon oxide, lanthanum oxide, lanthanumaluminum oxide, zirconium oxide, zirconium silicon oxide, tantalumoxide, titanium oxide, barium strontium titanium oxide, barium titaniumoxide, strontium titanium oxide, yttrium oxide, aluminum oxide, leadscandium tantalum oxide, and lead zinc niobate.
 32. The method of claim29 wherein said titanium carbide layer has a p-type workfunction. 33.The method of claim 29 wherein said titanium carbide layer has aworkfunction between about 4.9 eV and about 5.2 eV.
 34. The method ofclaim 29 wherein said titanium carbide layer has an n-type workfunction.35. The method of claim 29 wherein said titanium carbide layer has aworkfunction between about 3.9 eV and about 4.3 eV.
 36. The method ofclaim 29 wherein said titanium carbide layer has a mid-gap workfunction.